hiusa.org will link you Hosteling International. Then click on "International". No age max. I stayed in one when I was close to 60. (There is a max in Bavaria, but that is the only place of which I know.)
Easyhotel is simply
www.easyhotel.com .
And you could search on "couch surfing". Free. I've never done it, but have talked to people that have. Reports are that is is great fun and works well.
Romelle